Various manufacturing and performance considerations often make it desirable to include more than one semiconductor die in a single package. However, by including more than one die in a single package, various testing problems arise. For example, since it is relatively expensive to test semiconductor die separately before they are packaged, manufacturers sometimes perform a minimal amount of testing on individual die before those die are placed into a multi-die package. Because the individual die are not tested before they are packaged, the die must be tested together after packaging. While testing the die together after packaging is usually less expensive than testing each die separately before packaging, when one of the die in the multi-die package is defective, the whole multi-die package must usually be scrapped, resulting in the loss of other good die in that package.
Another limitation of testing multiple die in a single package is that the more die within a single package, the more complex the testing becomes. This added complexity requires more complex test hardware, and can limit the ability to thorough-test some portions of one or more die within the multi-die package. It would be useful, therefore, to know that each die used in multi-die packages was fully functional, without having to rely on expensive pre-package die testing.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the Figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the Figures to indicate corresponding or analogous elements.